As I always do when I'm making my own PCBs, I try to have as few tracks on the front side of the board as possible, and keep most of them on the back side. Single-sided boards are way easier to produce at home, and whatever needs to be connected on the second layer I just bridge with wires, instead of etching copper tracks.

This time I managed to do all connections of a two-string submodule on a single layer, so I decided to just copy-paste as many of those submodules as needed and call it a day, instead of retracing the board as a whole. That means I don't get one 8-pin connector as I planned in the beginning, but rather three 4-contact connectors for each of three 2-string modules, each having own power-in which can be weird. But hey, lots of electronics nowadays has weird proprietary connections, sometimes unnecessarily complicated. Mine at least has documented pinout, and the weirdness of connections is not purposefully made to cause confusion (looking at you, inkjet cartridges).

The positive side is that one can easily make 8-string version for contemporary metal guitar or a 4-string version for bass-guitar without much modifications. Just add or delete 2-string submodules, and move the relays just a little to fit the string spacing.